Recently, in order to achieve higher speed and higher capacity of radio communications, attention has been given to a communication technique using the MIMO (Multiple Input Multiple Output) system. In this MIMO system, plural transmission stream signals are propagated in space in different manner thereby to achieve improvement of transmission rate and signal quality. At the reception side, there is need to separate such plural transmission streams appropriately and obtain a reception signal. As a signal separating method for realizing preferable characteristics from the plural transmission streams, there is known a Maximum Likelihood Detection (MLD) signal separating method.
In this MLD signal separating method, out of all available symbol groups each of which is made of plural symbols in plural transmission streams transmitted simultaneously, a maximum likelihood symbol group is specified thereby to estimate plural transmitted symbols. Specifically, a symbol group of minimum distance between an actual reception signal and a symbol group affected by channel fluctuations (evaluated with a square of Euclidean distance in symbol constellation) is finally detected by the MLD signal separating method.
Besides, in this MIMO system, the AMC (Adaptive Modulation and Coding) system is performed in order to improve the throughput of the overall system by performing transmission at appropriate transmission rates in accordance with the channel state that varies with time. In this AMC system, a Modulation and Coding Scheme (MCS) is selected with which a suitable transmission rate can be achieved in accordance with the channel state.
In this MIMO system, there are plural transmission streams and they are transmitted in different channel states (channel paths). In order to simplify the processing of selecting an MCS for each transmission stream, there has been proposed a technique of preparing a table in which each of various MCSs is associated with a CQI (Channel Quality Indicator) (received SINR) and an error rate when it is assumed that the modulation scheme is equally used for all transmission streams and selecting an MCS in accordance with a CQI measured of each transmission stream (for example, see NPL 1).